1. Field of the Invention
This invention relates to the cleaning of the interior surfaces of conduits. More particularly, it relates to the enhanced in-situ cleaning of conduits having oily deposits on the interior surfaces thereof.
2. Description of the Prior Art
The Sandjet process is a well known and successful process for the in-situ cleaning of the interior surfaces of conduits used for the transport and/or processing of fluids, solids or a mixture thereof. The conduits thus cleaned include fired heater tubes used in hydrocarbon or chemical processing applications, pipelines heat exchange tubes and the like. In the practice of the Sandjet process for such in-situ cleaning operations, cleaning particles are entrained in a propelling fluid stream and are introduced into the conduit to be cleaned at a velocity sufficient to effect the desired cleaning action. For pipeline applications, the cleaning particles commonly employed generally comprise an abrasive material, such as flint, whereas in various other in-situ cleaning applications, cleaning particles such as non-angular, non-abrasive, steel shot may be advantageously employed.
In fired heater tube applications, the Sandjet process is used to decoke and clean the interior surfaces of furnace tubes, as is described in the Nunciato et al patent, U.S. Pat. No. 4,297,147, issued Oct. 27, 1981. As described therein the carrying out of the in-situ Sandjet process using steel shot cleaning particles provides significant advantages compared with the known alternative decoking approaches, such as turbining, hydroblasting and steam-air decoking. In addition to the advantages noted in the patent, there is a growing appreciation in the art of the energy savings that can be derived as a result of the decoking of furnace tubes by means of the Sandjet process as compared with the results obtainable by the most frequently used alternative approach, i.e. the above-mentioned steam-air decoking. The flexibility of the Sandjet process and its scope of application have been extended, particularly with regard to the removal of difficult-to-remove deposits, by the use of regular, non-random cleaning particles having less than spherical symmetry. Upon the propelling of such particles through the conduit to be cleaned, an advantageous balance of desired cleaning action and undesired erosion of the interior surfaces of the conduit is achieved, as is disclosed in C. B. Pollock et al, U.S. Ser. No. 377,788, filed May 13, 1982, now U.S. Pat. No. 4,482,392.
It is recognized, however, that further development and improvement are required in order to extend the benefits and advantages of the in-situ Sandjet cleaning process to an ever greater range of application. The inherent advantages of this in-situ approach are such as to create a desire, and even a genuine need, in the art for such development of the flexibility and the predictability of the Sandjet process as applied to applications presenting obstacles to the full and effective extension of said benefits and advantages thereof on a routine commercial basis. One cleaning application in which such development is desired pertains to the removal of oily or tar-like deposits that may accumulate on the interior surfaces of furnace tubes, pipelines or other conduits employed in certain services. It is often very difficult, if not impossible, to effectively remove such oily deposits by the economically feasible practice of the Sandjet process. The problem encountered is that a wet or oily deposit slows-down or captures the cleaning particles passing through the conduit obviating the effectiveness of the cleaning action. For this reason, the providing of Sandjet process services for the removal of oily deposits is commonly preceded by a steam and/or solvent wash of the oily deposit. It will be appreciated, however, that the necessity for carrying out such deposit wash operations adds appreciably both to the time and cost of the overall decoking or other cleaning operation, thus obviating some of the benefits sought to be derived from the in-situ deposit removal Sandjet cleaning process. The improvement of the Sandjet process with respect to the removal of oily deposits, therefore, would be of practical advantage in the art.
It is an object of the invention, therefore, to provide an improved process for the in-situ removal of oily deposits from the interior surfaces of conduits.
It is another object of the invention to provide an in-situ cleaning process obviating the need for the preliminary washing of oil deposits desired to be removed from the interior surfaces of furnace tubes, pipelines and the like.
It is a further object of the invention to enhance the effectiveness of the cleaning action of particles propelled through the interior of a conduit to be cleaned.